Various dehydrogenation processes have been proposed to dehydrogenate dehydrogenatable hydrocarbons such as cyclohexanone and cyclohexane. For example, these dehydrogenation processes have been used to convert at least a portion of cyclohexanone into phenol.
Phenol is an important product in the chemical industry and is useful in, for example, the production of phenolic resins, bisphenol A, ε-caprolactam, adipic acid, and plasticizers.
Currently, the most common route for the production of phenol is the Hock process. This is a three-step process in which the first step involves alkylation of benzene with propylene to produce cumene, followed by oxidation of the cumene to the corresponding hydroperoxide and then cleavage of the hydroperoxide to produce equimolar amounts of phenol and acetone.
Other known routes for the production of phenol involve the direct oxidation of benzene, the oxidation of toluene, and the oxidation of s-butylbenzene wherein methyl ethyl ketone is co-produced with phenol in lieu of acetone produced in the Hock process.
Additionally, phenol can be produced by the oxidation of cyclohexylbenzene to cyclohexylbenzene hydroperoxide wherein cyclohexanone is co-produced with phenol in lieu of acetone produced in the Hock process. A producer using this process may desire to dehydrogenate at least a portion of the cyclohexanone produced into the additional phenol depending on market conditions.
There are many methods for dehydrogenating various compounds into phenol. For example, U.S. Pat. No. 4,933,507 discloses that phenol can be produced by dehydrogenating cyclohexenone through a vapor-phase reaction in the presence hydrogen using a solid-phase catalyst having platinum and an alkali metal carried on a support such as silica, silica-alumina or alumina. In addition, Saito et al. discloses the use of palladium supported on various metal oxides (Al2O3, TiO2, ZrO2, MgO) as a catalyst in the dehydrogenation of cyclohexanone to phenol. See “Performance of Activity Test on Supported Pd Catalysts for Dehydrogenation of Cyclohexanone to Phenol (effect of supports on activity)”, Ibaraki Kogyo Koto Senmon Gakko Kenkyu Iho (1995), 30, pp. 39-46.
One problem that has been encountered in the use of supported noble metal catalysts in the dehydrogenation of compounds such as cyclohexanone is that the activity of the noble metal decreases fairly rapidly unless the metal is well dispersed on the support. However, a typical catalyst produced by directly impregnating a noble metal onto a support tends to result in poor metal dispersion because of non-uniform metal particle sizes. Thus, the resultant catalyst generally deactivates rapidly and so requires frequent reactivation or replacement. Given the high cost of noble metals and the loss in production time involved with frequent reactivation, there is therefore a need for a cyclohexanone dehydrogenation catalyst having improved resistance to deactivation.
According to the present invention, it has now been found that, by adding an amino acid or amino alcohol to the liquid vehicle used to deposit the noble metal onto the support, the dispersion of the noble metal on the support can be improved resulting in a more deactivation-resistant catalyst.
U.S. Pat. No. 7,538,066 discloses a supported multi-metallic catalyst for use in the hydroprocessing of hydrocarbon feeds, wherein the catalyst is prepared from a catalyst precursor comprising at least one Group VIII metal, a Group VI metal and an organic agent selected from the group consisting of amino alcohols and amino acids. The catalyst precursor is thermally treated to partially decompose the organic agent, then sulfided. The addition and subsequent partial decomposition of the organic agent is said to decrease the average height of the platelet stacks of the final sulfide catalyst.